In an apparatus of this type known from EP 0 441 949 B1, the individual program boards belonging to two stacks are pivoted next to each other in a chassis behind its two viewing windows around pivots located at their rear sides in such a way that they can be turned over individually by a rail movable to and fro by a drive which rail is provided with stops which engage at lug-shaped projections of the program boards extending beyond the pivots. Here, in each case two opened sides of each stack of the program boards become visible which sides lie diagonally on each side of each viewing window. According to the opened sides of the program boards assembled as racks in each case, the center migrates between two opened sides to the left or right in each viewing window because the pivots of the individual program boards are supported in a line next to each other fixed to the chassis and the row of pivots of each stack takes up a length corresponding to the breadth of the stack. Due to the migrating of the centerlines between the opened sides in the viewing windows, an unattractive appearance is created because the symmetry of the opened sides to the relevant viewing window is interrupted.
It is therefore the object of the invention to provide an apparatus of the type described above where the centerline between two opened program boards always remains at the same position in the center of the viewing window so that the two sides of the program boards always appear at the same place in the viewing window.